Elastic sheath cables



N. KLEIN ELASTIC SHEATH CABLES Filed Feb. 10, 1956 March 18', 1958PRESSURE SOUREZE CABLE THERMAL SWITCH R E T E M M A w United StatesPatent C ELASTIC SHEATH' CABLES Nicholas Klein, Haifa, Israel, assignorof one-half to The American Society for the Advancement of The HebrewInstitute of Technology in Haifa, Palestine, Inc., New York, N. Y., acorporationof New York Application February 10, 1956, Serial No. 564,798

16.Claims; (Cl..1484) The present invention relates generally tothemanufacture, transportation and laying of electric cableseand moreparticularly concerns electric cables having elastic sheaths subjectedto internal pressures.

It is well known in the art relating to electric'cables, to fabricateelastic sheath cables, operating under internal pressures. These cablesnormally utilize solidand liquid insulation materials, and gas filledcavities are carefully avoided. The. sheath cross-sections are normallynon-circular, elliptical and triangular shapes, being common, anda-minimurn-internal pressure is maintained at no load. As load isappliedthe temperature of such cables increases, with consequentincrease of internal pressure. The sheath distorts, in response to thisincrease in internal pressure, in such manner as to' increase the volumeof the cable, i. e. inthe case of a cable ofnoncircular cross-section,the cross-section becomes more nearly circular underload than it hadbeen under no load.

The continued operativeness of the cable, and its safe functioning,requires that all, deformations be reversible, i. e. that the cable andparticularly the sheathreturn to its original shape when theinternal'pressure is decreased on no load. This condition is met if thegreatest strain introduced on full cable load remains below the elasticlimit for the cable and particularly. for the sheath material.

It follows that the current carrying capacity of; an elastic sheathcable is a direct functionof the permissible temperature increase of thecable under load. Thelatter is proportional to permissbilevolumeincrease, whichin turn depends on the elastic limit of the sheathmetal.

The elastic limit of various metals, in the pure, v soft state, is foundto be less than,0.0005. Calculations show values of 0.0015 to bedesirable. Such values of elastic limit are found only in metals whichhave been in some degree hardened. It follows that materials suitablefor elastic sheath cables must be harder by a'considerable factor thanmaterials employed for sheathing ordinary cables. The latter being soft,can be readily transported on drums, unwound, and layed. Pressurecable,.having hard elastic sheathing, cannot be transported in drums toa desired location, unwound, and layed.

it is the primary object of the-present invention to provide a novelmethod of fabrication, transportation and laying of elastic sheathpressurecables.

It is a further object of the. invention to provide a methodof sheathedcable fabrication, transportation and laying,v while soft, followed bysheath hardening treatmentafter the, cable has been laid, and While, insitu;

It is another object of' my invention toproduce a hardened" sheath in asheathedcable, after, thecable has. been laid.

h abo e and still. u er. f atures qbiaqts an advantages ofthe inventionwill become apparent upon considerationoiitheiollowing.detaileddescription of a specific embodimentot theinvention,especially-when ice 2 taken in conjunction with theaccompanying drawings, wherein:

Figure lis-a functional diagram" of a system for'work hardening cablesheaths, in situ; and

Figure 2 is a functional diagram of a system for heat hardening cablesheaths, in situ.

Briefly describing now the present invention, a cable is sheathed, in afactory, by any desired method, with ametallic sheath, the metal beingcapableof hardening. The cable is then transported, on drumsorotherwise, and laid, whilethesheathis unhardened. Afterthecable hasbeen laid ity is subjected to repeatedinternaltvariations ofpressure,.or. to temperaturevariations, sufilcient to cause hardening;the procedure being repeated, as necessary, .until the. desired .elasticlimit hasbeenattained for the sheath.

In the. alternative. the hardening may be partially. accomplishedbyswaging inasitu. andcompleted'by repeated pressure variations vor by.heating.

If desired the cable may be lead sheathed at the factory, andthe leadmay be removed and-the final sheath materiaLsuhstituted, after, thecable has been laid. Thisobviates the possibility thatthefinal elasticsheath material will be subjected to age hardening, ortoinadvertenthardening, before: being, laid.

WORK HARDENING In the, case of metals, hardenabletby Work hardening, thecable, as 1, is sheathedat the factory with a metal sheath 2, ofsuitablethickness, while. the metalisinits soft, annealedstate, utilizing anyknown method-offabrication. The, cable istransported to1the laying site,on drums or the like, and laid. The sheathmay be-oversize at thispointin the procedure, in Whichcase it may be swaged down in situ,causingpartial work hardeningyor the sheath may be originallyofsuitablesize. Further, if desired the cable. may be leadsheathedpreliminarily at the factory, and after laying the lead sheath may beremoved and the final sheath applied.

Assume the sheath 2 to be fabricated of aluminum alloy 545 containing3%% Mg and /3% Mn, for example only. The-elastic limit is, for thismetal, 7,000. lb./sq. ,in. To the cableis connected during workhardening a. plurality of oil reservoirs 3,.at'suitable lengthstherealong, which serve to keep the cable 1 filled with oil. To the oilreservoirs 3 is connected. at pressure line 4, filledwith oil, andconnected to a pressuresource 5 and a control valve 6, whichpermits'application of any desired, degree of pressure to the line 4,and thence to the oil'reservoirs 3, and the interior of, the cable Thelatter isof course, closed at its ends, andtogether with the requiredjoints constitutes a closed system., Thepressure applied from source 5may be measured, as by a meter 7,' and. if desired, meters may beemployed in conjunction with the oil reservoirs 3. In any event,pressure is propagated rapidly along the cable, because low viscosityoil is employed, and the oil paths in, the cableand inthe pipe line 4are relatively large.

The largest stresses produced in sheath 2 during cyclic applicationofpressures, always exceed the elastic limit of the sheath by about 10%.So, the first pressure may be about 7700 lb./sq. in., and eachsucceeding cycle of pressure may represent-a further increase of 10%,untila final pressure 17,500 lb./sq. in. has been attainedgand attained.

1 alloys, preferably of the non-magnetic type, and containing highpercentages or chrominum. and nickelmay also be employed. 1 i

. HEAT HARDENING L Certain metals which are isiuitablejfor cable'sheaths are susceptible of hardening, by heatf'treatment 'The cable maybe laid in soft state, and hardened in situ by heat treatmentuntil therequiredelastic limithas been In this procedure care must be, taken notto reach temperatures atiwhichcable'insulation' will berdamaged. Thislimitation requires that temperaturesnot to exceed 120 C. beemployed,'and in consequence the procedure requires several hourstocomplete. Heat may be applied to the cable by causing electric currentto flow directly in the sheath or in-metal tape wound about the sheath.7 A W V p A specific example of heat hardening is described for elasticsheath cables, employing aluminum alloy 268 as a sheath metal. Thisalloy contains'4% 'Cu, Si, %%'Mn,and /2%Mg.' U

Referring now more particularly -to'Figure 2 of the accompanyingdrawings there isillustrated a cable 1, having'a heat hardenable sheath2. A source, of electric current 13 such as a generator, causes currentof measured amount to fiow directly in the sheath 2, the

return path for the current beinga line 14. In series with the line 14,at several points therealong; are thermally responsive circuit breakers15, 16, which trip when the cable sheath 2 attains a predeterminedtemperature.

In essence then, the circuit breakers 15, 16 are thermoa staticswitches, normally closed, and which, open when sufliciently heated.Such switches are, per se, well known and commercially available, andmay be placed in contact with sheath 2 at several positionstherealong,to assure.

that no'hot spots will develop in the cable, and damage same.

, The switches 15, 16 may be equipped with indicators of temperature, as17, 18, so that current in the cable may be controlled, as desirable, tomaintain required temperatures, and heating cycles of from 2 to 10 hoursmay be required. V 7

The abovedescribed heat hardening treatment maybe applied to sheathsfabricated of a large variety of agehardenable alloys of aluminum,copper and iron, and more specific mention may be made of. alloyscontaining beryllium, nickel and silicon, nickel and aluminum, aluminumbronzes.

In the following table are provided data concerning 'representativealloys, preferred methods of hardening in situ, and certain pertinentphysical factors;

Table I.Continued Proportion- Stress in ality limit lb./sq. in. B.Alloys for heat treatment in ibJsq. in. when strain after full heat0.0015 treatment,

Aluminum 268 0117475, Si M11 I 40,000 15, 000 Aluminum S-Zn 6%, Mg 2%%,Cu 56%,

M11 Cr 50, 000 '15, 000 Beryllium C0pper-1.75 to 2.5%"Be; some 00, kg,etcMg.. 7; i.a; 90, 000 24,000 Silicon' 0nze 1.5 u, i V e, I

znu g. 50,000 24, 000 S ecia lass-72.5 u 20 n, '6 i 1.5% A1 Zinnia?45,000, V 23,000

While I have describedsp'ecific and preferred embodiments of my'invention, as required by the applicable statutes of the United States,modification of general arrangement, and of detail may be resorted towithout departing fr om the true spirit ofthe invention, as defined inthe appended claims WhatIclaimisc i. A method of fabricating,transporting and laying sheathed pressure cable comprising the steps of:(l) fabricating, transporting and laying a sheathed pressure cable, thelaid cable having a relatively soft but hardenable metallic sheath; (2)hardening said metallic .sheathin I situ.-

2. The method in accordance'with claim 1 wherein said hardening is heathardening.

3. The method in accordance with claim 1 wherein said hardening is workhardening; V 4. A method of cable making, said cable. beingpressurized'internally and having ametallic sheath, comprising the stepsof:. (l) establishing said cable in situ, $aid cable when so'estabiishedhaving a relatively soft sheath, V

and (2) hardening said sheath in situ by repeated appli cations ofinternal pressure exceeding the elastic limit of said cable by 'a factorofthe order of about 10% in I each of a plurality of applications. untilthe elastic limit of said sheath exceeds. apredetermined value. n 1 5.Themethod 'of cable making, saidcable bein'g pressurized internally andhaving a metallic heat hardenable.

sheath, comprising 'the steps-of: (1) establishing said cable in situ,said cablewhen so established having a'relatively soft sheath, (2)hardening said sheath 'in situ by application of heat to said sheathuntil a predetermined elastic limit has been attained. I

6. The method. of cable making and laying, said cable having a sheathofjdeforinable metal of fab'ricatednoncircular cross-section,thejstepsof: (1) establishing said cable in situ while saidsheath isinlrelatively soft and pliable state, (2) hardening said sheath in situuntil the elastic limit of said'sh'eath is, of .0025 according to need.

7. The combination in accordance the order of .001 to for a1peri0d ofapproximately from 210 hours, at-a temperature of not greater thanrl20centigrade.

8. The combination in accordance with claim 6'wherein'said hardening is"accomplished by work hardening,

above its elasticlimits, as said limits increase due to 7 applicationsof 'said pressure. r a 9. 'A method of cable makingand laying,said'cable being pressurized internally and having a metallic non-.

': ferrous sheathjcomprising' the steps of: (1) establishing alloy.

Table I V Proportionality Stress in 1 limit in lb./sq.'i.n. Ib./sq. in.,

A. Alloys for work hardening whegl soft hard Aluminum 54S-Mg 3%%, Mn 7,000 15, 000 Aluminum SSS-Mg 5%, Mn 15, 000 .4.-. 15, 000 Highconductivity copper 2, 000 27, 000 24, 000 Brass65% Cu, 35% Zn; 9, 00040, 000 21, 000 Aluminum brass-76% Cu, 22% Zn, I r 2% Al 9, 000 V 36,000 22, 000

' Aluminum bronze-92% Cu, 5% Al,

' 3% Mn andNi. e 9, 000 45, 000 f e 24, 000 Copper -Niekel80%- Cu, 20% N40,000 29, 000 Monel 38,

Austenitie steel-18% Cr, 8% Ni. roughly 29,000 correi spgnodfig to astrain o said cable in'situ while said sheath is soft and pliable; and(2) hardening said sheath in situ.

' '10. The combination according to claim.9 wherein said metallicnon-ferrous sheath is' fabricated of jan 11. The combination said alloy"includes primarily aluminum.

with claim 6.where in said hardening is accomplished by heat hardeningaccordingto claim ,10 wherein;

12. The combination according to claim 10 wherein said alloy includesprimarily copper.

13. A method of cable making and laying, said cable being pressurizedinternally and having a metallic sheath, comprising the steps of: (1)establishing said cable in situ while said sheath has an elastic limitof the order of 0.0005, and (2) hardening said sheath in situsufficiently to establish an elastic limit for saidsheath of the orderof 0.0015.

14. The combination according to claim 13 wherein said hardening isaccomplished by the application of heat.

15. The combination according to claim 14 wherein said heat is notgreater than 120 centigrade, and is applied for a period of from two toten hours.

16. The combination according to claim 15 wherein said heat is appliedby conversion of electrical energy into said heat.

References Cited in the file of this patent UNITED STATES PATENTS1,395,474 Bray Nov. 1, 1921 1,834,128 Langerberg Dec. 1, 1931 1,891,234Langerberg Dec. 26, 1932 1,926,545 Koch Sept. 12, 1933 2,044,763 Boutonet a1. June 23, 1936 2,197,609 Cornell Apr. 16, 1940 2,615,411 Clevengeret a1. Oct. 28, 1952

1. A METHOD OF FABRICATING, TRANSPORTING AND LAYING SHEATHED PRESSURECABLE COMPRISING THE STEPS OF: (1) FABRICATING, TRANSPORTING AND LAYINGA HEATED PRESSURE CABLE, THE LAID CABLE HAVING A RELATIVELY SOFT BUTHARDENABLE